The present invention relates to a fail safe thrust reverser door lock that will hold a thrust reverser door of an aircraft jet engine close to its forward thrust position on the occasion of a malfunction in the primary door locking mechanism.
Thrust reversers for aircraft jet engines are, of course, well known in the art and typically such thrust reversers alter the normally rearward flowing propulsive gases into a direction having a reverse thrust component to decelerate the jet aircraft. Thrust reversers are usually incorporated into the cowling of the jet engine and comprise one or more movable panels that are movable between a forward trust position and a reverse thrust position. In their forward thrust positions, the panels cover one or more reverse thrust openings passing through the cowling, while such openings are uncovered when the panels are moved to their reverse thrust positions such that at least a portion of the propulsive gases are directed outwardly through the reverse thrust opening.
As can well be imagined, unintended deployment of the thrust reverser panel toward its reverse thrust position can be catastrophic during aircraft flight. Therefore, thrust reverser panel locking systems typically employ redundant locking mechanisms which may comprise a primary lock, a secondary lock and a tertiary lock. The functions of the secondary and tertiary locks are to hold the thrust reverser panel close to its forward thrust position upon malfunction of the primary lock. The secondary and tertiary door locks may be associated with the actuator for moving the panel between its forward thrust and reverse thrust positions, or may be located on different areas of the thrust reverser panel than the primary lock.
The secondary and tertiary, or emergency, locks must provide a substantial clearance, on the order of several mm, between a lock bolt and a strike plate in order that the engagement and disengagement of these elements does not hamper the operation of the thrust reverser panel, or the primary lock. Thus, on the occasion of an accidental malfunction of the primary lock, before the emergency lock becomes effective, the thrust reverser panel tends to move away from the forward thrust position until the clearance between the lock bolt and the strike plate of the emergency lock is taken up. This movement of the thrust reverser panel causes an impact between the lock bolt and the strike plate of the emergency lock with a release of kinetic energy proportional to the clearance "e". This impact applies additional stresses of at least twice the static stress F.sub.0 to the emergency lock that it would have to withstand it if were operating without the clearance. To withstand these additional stresses, the thrust reverser structure must be reinforced in the vicinity of the stationary cowling, the movable thrust reverser panels and the locking components, thereby increasing the weight of the assembled thrust reverser and increasing the cost of manufacture and operation.
The problems caused by the additional stresses imposed upon the emergency lock are acute in regard to the pivoting door, or target-type thrust reverser wherein the thrust reverser panels comprise doors pivotally attached to the cowling such that a forward portion of the door pivots outwardly from the cowling in the reverse thrust position. In such thrust reversers, the doors are subjected to the pressure of the propulsive gases acting on the inner surface of the door which add substantially to the kinetic energy of the door upon malfunction of the primary lock. Also, once the door moves away from the forward thrust position, its forward portion is acted upon by the ambient airflow flowing over the external surfaces of the cowling which produces an additional force on the door tending to move it toward the reverse thrust position and consequently increasing the kinetic energy of the door until the clearance of the emergency lock is taken up.
The problem is also applicable in a cascade-type thrust reverser wherein the thrust reverser panel slides in a direction generally parallel to the longitudinal axis of the cowling from a forward, forward thrust position to a rearward reverse thrust position and to the "scoop" thrust reversers in which the panel comprises doors pivotally attached to the cowling in which the forward portions of the doors move radially inwardly into the gas flow duct when in the reverse thrust position.